1. Field of the Invention
The present invention relates to a control system of an electric actuator and a control method thereof, in which drive of the electric actuator is controlled by a plurality of controlling units.
2. Description of the Related Art
Japanese Laid-open (Kokai) Patent Application Publication No. 2005-224068 discloses a control system including a VEL controller and an engine control module (ECM). The VEL controller controls an electric actuator (motor) for driving a Variable Valve Mechanism (VEL mechanism) in which Valve lift amounts and valve operating angle of inlet and exhaust valves of an engine are variable. The engine control module controls each device of the engine. In the control system, the ECM computes a target valve lift amount to output the target valve lift amount to the VEL controller, and the ECM diagnoses control abnormality of the VEL controller to input a signal indicating the diagnostic result and an output signal from the VEL controller into an AND circuit. When both the signals input into the AND circuit correspond to a normal state, an electric power is supplied to a drive circuit of the electric actuator. When at least one of the signals input into the AND circuit indicates abnormality, the electric power supplied to the drive circuit is cut off.
In the control system as disclosed above, the electric power supplied to the drive circuit is cut off when at least one of the signals input into the AND circuit indicates abnormality, so that a mistaken control of the electric actuator can be prevented. However, when a circuit which outputs the signal to the AND circuit breaks down to maintain a signal indicating the normal state, sometimes the electric power supplied to the drive circuit cannot forcedly be cut off although the abnormal diagnosis is made.